The present disclosure relates to detecting anomalies, defects or damage in a structure or structural health monitoring of a structure, such as an aircraft, civil structure or other structure, and more particularly to a method and system for identifying the mode of a Lamb wave being transmitted through the structure for structural health monitoring or detecting anomalies.
Determining the particular mode of a Lamb wave being propagated or transmitted through a structure to monitor the structural health of the structure or to detect any anomalies using direct measurement techniques typically involves placing two piezoelectric transducers on the structure. The transducers must be on opposite sides of the structure being monitored or evaluated. Additionally, the transducers have to be exactly opposite one another to accurately measure the phase of the Lamb wave during passage of the Lamb wave through the structure at the location flanked by the opposing transducers. By observing the response of each of the transducers, a determination can be made about whether the wave sensed on each side is either in-phase, which indicates the symmetric (S0) mode, or out-of-phase, which indicates the asymmetric (A0) mode. This method or technique may be prohibitive in some structural health monitoring (SHM) applications. For example, it may not be possible to place transducers on both sides of a structure or exactly opposite one another. This technique also requires additional transducers, wiring and electronics resulting in additional cost and complexity of the system.